Theaters across the United States are on high-alert and imposing new security measures in the wake of the Colorado shooting during a midnight screening of Warner Bros.' The Dark Knight Rises.

At least 12 people were killed and dozens more injured when suspect James Holmes -- his hair painted red and calling himself the Joker -- opened fire on the audience at a Cinemark multiplex in Aurora around 12:30 a.m. Friday. Details are still emerging, but the heavily armed 24-year-old man apparently used an emergency exit at the front of the theater.

The tragedy has left the film industry reeling and exhibitors rushing to implement new security measures. Police departments in major cities -- including Los Angeles and New York -- will have a heavy presence in theaters this weekend, an unusual sight.

Also, some costumed customers will have a hard time gaining access. AMC Entertainment is banning face-concealing masks and fake guns, while Regal will have stricter controls on attire (initially, AMC banned all costumes).

At this time, neither Warner Bros. nor theater owners have announced any plans to stop playing Christoper Nolan's final Batman pic, which is doing monster business at the domestic box office despite the tragedy.

"At this time, our show schedules circuit-wide will not change. We will not allow any guests into our theatres in costumes that make other guests feel uncomfortable and we will not permit face-covering masks or fake weapons inside our buildings. If guests wish to exchange or refund any tickets, we will honor our existing policy and do as our guests wish. We are taking necessary precautions to ensure our guests who wish to enjoy a movie this weekend can do so with as much peace of mind as possible in these circumstances," AMC said in a statement.

Regal customers also can expect to have purses and smaller bags checked, according to one exhibitor. Regal isn't officially commenting on specific procedures, such as checked bags.

A spokesperson for the Los Angeles Police Department told THR that the department will deploy extra uniformed officers to venues throughout the city. Undercover police officers also will conduct spot checks in theaters.

Undercover officers "will walk in, sit next to regular citizens. They won't stay for the entire movie but they will be looking for anything out of the ordinary," the spokesperson said.

Even the upscale ArcLight Cinemas in Southern California is clamping down. "Screenings of Dark Knight Rises will continue as planned. For the safety of our guests, we have increased security on-site at all locations," the exhibitor tweeted.

The Aurora shooting is the worst in the history of cinema. In 1999, three people were killed during a screening of The Matrix, among other isolated acts of violence.

On Friday morning, the National Association of Theater Owners was in close touch with the Department of Homeland Security, author of a long checklist of security procedures for theaters and other public venues.

Exhibitors overseas are likewise imposing new security measures. Dark Knight Rises opens day and date in 17 foreign markets this weekend, including in the U.K. and Australia.